Exploring the Performance of High and Low Temperature Chambers Under Extreme Conditions

I.The principle of high and low temperature test chamber alternating wet and heat test box:

Under high and low temperature test chamber, due to the steam added is not fully mixed with air or contact with the box wall and local condensation, not only the added steam amount decreases, but also releases heat to make the temperature of the humid air inside the box rise: In addition to the above e ‘> e. So it is not a isothermal humidification process, and the temperature inside the box will rise.

LISUN High Low Temperature Chamber | Thermal Chamber | Climate Chamber is according to IEC60068-2-1 (GB/T2423.1) and IEC60068-2-2 (GB/T2423.2), IEC60068-2-78, IEC60598-1, GB/T2423.17, GB/T5170.2, GB/T5170.5. The climate chamber is used to test the CFL/LED which meets IES LM-80-08, electricity products, automative cars, home appications and mobiles.

II.The principle of high low temperature test chamber:
When air passes through an open water surface, thermal and wet exchanges occur with the water surface. Depending on the water temperature, only sensible heat exchange may occur; Wet exchange and latent heat exchange may also occur, in addition to sensible heat exchange, which is the result of evaporation (or condensation) of water vapor molecules in air and absorption (or release) of latent heat of vaporization. The total heat exchange is the algebraic sum of the sensible heat exchange and latent heat exchange.

When air and water are in direct contact, the temperature of the saturated air boundary layer close to the water surface is equal to the water surface temperature, and the concentration of vapor molecules or the vapor pressure depends on the saturated air temperature of the boundary layer.

If the temperature of the boundary layer is higher than that of the air above it, heat is transferred from the boundary layer to the air; Conversely, heat is transferred from the air to the boundary layer. If the vapor concentration of the boundary layer is greater than that of the air above it (i.e., the vapor pressure of the boundary layer is greater than that of the air), the number of vapor molecules in the air will increase; Otherwise, it will decrease. The former is called “evaporation”, and the latter is called “condensation”. In the process of evaporation, the vapor molecules missing from the boundary layer are replenished by the water molecules leaping out of the water surface; In the process of condensation, too many vapor molecules in the boundary layer will return to the water surface.

It can be seen that the sensible heat exchange between air and water depends on the temperature difference between the boundary layer and the air above it, while the wet exchange and the subsequent latent heat exchange depend on the difference in vapor concentration or vapor pressure between them.

The principle of wet and heat: Electric heating water to produce steam in the water tank, steam into the wet and heat box through the spray pipe to humidify the air in the box.
High pressure steam from the steam boiler is reduced and sprayed into the wet and heat box for humidification.

In high and low temperature test chamber, air flow passes through the shallow water surface of the box, the temperature of this surface is equal to the saturated air boundary layer for wet heat exchange. When the vapor concentration in the boundary layer is greater than the vapor concentration in the air flow passing through, it is humidification, otherwise it is dehumidification.

III. High and low temperature test chamber test methods:
There are many ways to represent the humidity of high and low temperature wet heat test box, as far as the test equipment is concerned, usually use the concept of relative humidity to describe it. The definition of relative humidity is the ratio of the vapor pressure in the air to the saturated vapor pressure at this temperature, expressed in percentage. According to the property of water vapor saturation pressure, the saturation pressure of water vapor is only an index of temperature. It is unrelated to the air pressure of water vapor. The process of humidification is actually to increase the vapor pressure, and the initial humidification method is to spray water into the test box, and control the water flow to control the saturation pressure of the water surface. The water forms a large surface on the surface of the box, and humidifies the box through diffusion. The relative humidity in the test box increases.

At that time, the humidity was mostly controlled by a simple switch control with mercury contact gauge. For large latency hot water tank temperature control, the adaptation is poor, so the control transition process is longer, can not meet the need of more humidification requirements for alternating wet and heat test box, more importantly, when spraying on the box wall, inevitably water droplets on the test items to the test items for different degrees of pollution. At the same time, there are certain requirements for drainage in the box. This method was soon replaced by steam humidification and shallow water pan humidification. But this method still has some advantages. Although the control transition process is longer, the humidity fluctuation is small after the system is stable, which is suitable for high and low temperature wet heat test box.

In addition, during the humidification process, the steam does not increase the additional heat in the system. Also, when controlling the spray water temperature to lower than the test point temperature, the spray water has a dehumidification effect.

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